1. Field of the Invention
The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus having a member for pressing a print head element against a platen roller.
2. Background Information
Also, heat transfer printers are known as an example of an image forming apparatus. Such conventional image forming apparatus includes a print unit pivotably supported to a chassis, and a platen roller rotatably supported to the chassis. The print unit is normally urged in a direction away from the platen roller by a torsion coil spring, and is pressed against the platen roller by pressing members. The pressing members are pivotably supported to the chassis via an axle. One of the pressing members is pivoted by a motor. The pivoting of the pressing member is transmitted to the other of the pressing member via the axle, which is coupled to the pressing members relatively unrotatably. Accordingly, the pressing members together apply pressure to the print unit.
As shown in FIGS. 17 and 18, the axle 105 has insertion parts 105a and formed near both ends of the axle 105 in oval shapes. The insertion parts 105a are tightly and relatively unrotatably inserted respectively into oval-shaped insertion holes 106a and 107a of the pressing members 106 and 107. Also, bearing supports 105b are formed at the ends of the axle 105, at the outer sides of the insertion parts 105a. The bearing supports 105b are rotatably supported in the insertion holes of the chassis. Press springs 106b and 107b that exert pressure on the print unit 102 are mounted on the pressing members 106 and 107, respectively.
FIG. 19 is a schematic side plan view illustrating the operation in which the print unit applies pressure to the platen roller. Since the pressing members 106 and 107 are mounted on the axle 105 tightly and relatively unrotatably, the axle 105 and the pressing member 107 shown in FIGS. 17-18 are pivoted as the pressing member 106 is pivoted by the motor. The print unit 102 is thereby pressed on by the press spring 107b of the pressing member 107, as well as by the press spring 106b of the pressing member 106. As a result, the thermal head unit 102b of the print unit 102 is pressed against the platen roller 103 despite the urging force of the torsion coil spring 109.
The conventional heat transfer printer shown in FIGS. 17 through 19 requires the two pressing members 106 and 107 with the respective press springs 106b and 107b, and the axle 105 are provided to press the thermal head unit 102b against the platen roller 103. Thus, the number of components required for pressing the thermal head unit 102b against the platen roller 103 is large. Furthermore, since the torsion coil spring 109 is required to urge the thermal head unit 102b away from the platen roller 103, the number of requisite components is even greater.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming apparatus that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.